1. Field of the Invention
The invention is directed to a therapy apparatus for the treatment of tissue in the body of a life form with ultrasound and is also directed to an operating method for treating benign prostate hyperplasia with such a therapy apparatus.
2. Description of the Prior Art and Related Subject Matter
Therapy apparatus of the type described above are used, for example, for treating benign prostate hyperplasia (BPH=benign enlargement of the prostate due to cell multiplication with progressive constriction of the urethra, increasingly occurring with age in men from about age 50). For therapy of BPH, less invasive methods are being increasingly proposed and investigated as alternatives to the classic method of operation and transurethral resection. For example:
Hyperthermia of the prostate by heating to 45.degree. C. with microwaves via a rectal applicator (U.S. Pat. No. 4,601,296) or via a urethral applicator (U.S. Pat. No. 4,967,765); PA1 In a modified form (higher temperature) as thermotherapy in combination with ultrasound imaging and cooling of the urethra (European Application 0 459 535); PA1 Transrectal irradiation with focused ultrasound and ultrasound imaging (U.S. Pat. No. 4,955,365); PA1 Non-invasive irradiation with ultrasound using an applicator constructed according to the "crossfire" principle and temperature measurement in the target region; PA1 Non-invasive irradiation with focused ultrasound with ultrasound imaging (European Application 0 170 416); and PA1 Laser treatment via a urethra probe (PCT Application WO 90.13333). PA1 sensitive structures such as the urethra in the case of the prostate are protected by cooling and/or PA1 a measurement and/or monitoring of the ultrasound ensues before and potentially during the therapeutic acoustic-irradiation (insonification) on the basis of at least one miniaturized acoustic pressure sensor (hydrophone) introduced into the tissue, preferably into the urethra in the case of the prostate and the location and/or orientation and/or drive of the source of therapeutic ultrasound is/are varied as warranted after comparison to the values desired at this location.
In thermotherapy, an over-heating of a larger volume of the prostate with following necrotization is to be effected. The treatment ensues over a time span of minutes through approximately one hour. Due to the irradiation, the tissue in the region to be treated is heated to temperatures above 45.degree. C. through approximately 60.degree. C. and is maintained thereat, so that damage with the goal of a reduction of the multiplied tissue is effected. In the case of hyperthermia, by contrast, a temperature of 45.degree. C. is not exceeded, or is at least not significantly exceeded.
A relatively sharp limitation of the zone of action and an elimination of regions to be generally treated is desired when heating is accomplished with microwaves because of the usually radial, symmetrical emission pattern of microwave antennas with an intensity that slowly decreases with increasing distances from the antenna. In addition to the cooling of the urethra, for example, the employment of radiation-reflective liquids has been proposed (European Application 0 370 890) for this purpose. A continuous monitoring of the resultant heating ensues with temperature probes introduced into the rectum and urethra. Complicated fiber-optical thermometers are thus required in a therapy apparatus working on the basis of microwaves.
Limiting the heating effect to the prostate is unsatisfactory in hyperthermia with transrectal applicators. Thermal damage of tissue outside the prostate can occur.
Like the effect of microwaves, the effect of focused ultrasound is likewise predominantly thermal and leads to necroses having an expanse of approximately 2 mm in diameter and 20 mm in length. A plurality of necroses must be produced side-by-side for a volume treatment. The identification of the target with an ultrasound image only supplies a two-dimensional tomogram with the standard technique. Three-dimensional presentation requires a high outlay for apparatus and time and is not yet clinically available. A complete identification of the position of the therapeutic zone of action of the ultrasound is only possible after a time during which damage will already have occurred.